top-trader-1

Had been running good for some time but have noticed a Low RPM stumbling that is getting progressively worse over the months.

96 LT1 / 80,000 miles .. No MIL codes are noted and Engine idles smooth

-- replaced MAP sensor and MAF


1) Most noticeable around 45 / 50 @ 1200 RPM and a slight throttle increase.

2) IS not noticeable in closed loop / prior to warm up.

3) When fully warmed up and on the road, if RPM is low and WOT, engine will stumble and may die.

4) If RPM is higher than ~ 2000 while in neutral while warm and WOT is hit, engine may stumble a little but will not die.

5) WOT and full power during drive time are OK as long as engine RPM is higher than ~ 1200

6) When the problem is occurring, for example, when I go WOT and RPM is low, it sound like a few cylinders are misfiring.

This does not seem to be a fuel problem and the MAP and MAF has been replaced with no significant difference.

Any suggestions before I replace the opti spark unit ?

Thanks in advance.

DVNCI

Has the car been modified and/or tuned before?

I would pull all the plugs and see how they look.

darkstallion_69

My car does exactly the same thing and I mean exactly the same it happened right after I accidently wet the optispark by mistake. I'm changing the optispark soon

78pacer

Let me know what you find. My '95 will chug and knock at low rpm in 6th gear while trying to accelerate. Sounds and feels as if I had the wrong grade gasoline in it, but that's not the issue. I don't want to toss $$ at it hoping to fix it.
Mike

96GS#007

One or a combination of the following...

Plugs
Plug wires
Opti

Pretty easy to inspect the first two.

runner140*

Before we blame the Opti, when was the last time the fuel filter was changed? Many other areas should be checked first. There are some Opti's out there with over 150,000 miles.

onedef92

You should check your fuel pressure, too. Could be an injector(s) issue.

colorlaserprinters

Im having very simialar issues on my 1994 lt1 vette. Its not bad enough it stalls though. But it acts up the same exact way otherwise.

SH-60B

Because this only happens once the car is warmed up in closed loop and using signals from its sensors to run the motor, there's a problem with one of the sensors. You can do resistance tests etc. to narrow down the culprit. For example, simply unplug the egr to test.

puterami

+1
This was actually my first thought.

mikey

I would suspect either o2 sensor or optispark. My opti developed a crack in the housing and when it warmed up things spread far enough to make it run erratically.

93QuasarBlue

SImilar issue. Drove it after a rain on wet road after Henri blew through, it started to sputter sitting in drive at idle. but not noticeable in neutral. it must have kicked some mist up to the opti.. after I washed the engine one day I drove it with the hood unlatched and woosh it seemed to clear up.

DKlettke

Similar problem here too. Replaced the plugs, wires, opti (it got wet), ICM, IC (it died a couple years ago), injectors (that solved another issue) and even the IAC. Still idles too low. I still have the drivers side o2 sensor to replace, i can't seem to get that off without a lift.